The present invention relates to a stacked secondary battery formed by sealing battery element including a multilayer structure prepared by laying flat plate-shaped positive electrodes and also flat plate-shaped negative electrodes one on the other by way of separators.
Lithium ion batteries are being broadly employed for portable equipment designed to be driven by a battery such as mobile phones because lithium ion batteries have a large charge/discharge capacity. Additionally, there is a large demand for high efficiency secondary batteries that can find applications in the field of electric vehicles, electric bicycles, electric tools and power storages.
Stacked batteries prepared by laying flat plate-shaped positive electrodes and flat plate-shaped negative electrodes one on the other by way of separators are broadly being employed in such high output power batteries. Positive electrodes prepared by applying lithium transition metal complex oxide particles to aluminum foil that operates as collector with an electro-conductivity providing material such as carbon black are employed in lithium ion batteries.
On the other hand, negative electrodes prepared by applying slurry of carbon particles and an electro-conductivity providing material such as carbon black to copper foil that operates as collector are employed there.
Stacked secondary batteries including lithium ion batteries are produced by covering battery element, which include a multilayer structure prepared by laying flat plate-shaped positive electrodes and flat plate-shaped negative electrodes one on the other by way of separators, by means of a film casing except an electrolyte injection port, sucking gas from the inside to produce a decompressed condition in the inside of the battery and then sealing the film casing.
The electrodes of lithium ion batteries can be deformed to degrade the efficiency of the battery as the active substance of the battery is forced to dope and undope lithium ions repeatedly in repeated charging and discharging operations.
In order to prevent positive electrodes and negative electrodes from being deformed due to repeated charging and discharging operations, for example, JP-A-2004-355915 proposes a battery comprising plate-shaped members, each of which has a metal plate at the center thereof and insulating resin arranged around the metal plate, that press from opposite sides of the battery element, which includes a battery element rolled body produced by rolling a multilayer structure of positive electrodes and negative electrodes laid one on the other by way of separators.
However, strip-shaped members including positive electrodes, negative electrodes and separators are laid sequentially one on the other in the order of separator/positive electrode or negative electrode/separator/negative electrode or positive electrode, whichever appropriate, to produce such a rolled body, which is then pressed to become flat with an outermost separator arranged as outermost peripheral member. Thus, the plate-shaped members that pinch the battery element between them contact the latter by way of the outermost separator and hence are thermally bonded to the latter only insufficiently. Documents that describe an arrangement of laying plate-shaped members one on the other as battery element are known. However, how the plate-shaped members are used to press the battery element is not clearly described there.
Therefore, it is an object of the present invention to provide a stacked secondary battery such as stacked lithium ion battery formed by laying flat plate-shaped positive electrodes and also flat plate-shaped negative electrodes one on the other by way of separators that shows a good heat radiating performance for the heat generated by charging and discharging operations and/or applied externally and is free from degradation of the charging/discharging characteristics thereof due to wrinkles produced to the separators by repeated charging and discharging operations that give rise to expansions and contractions.